Treatment of residual liquors



L, BRADLEY ET AL TREATMENT OF RESIDUAL LI QUORS.

Nov. 24, 1931.

Filed Jan. 14, 1924 \powwwaEou 3 INVENTORS BY PMM W ATTORNEY-.

Patented Nw 24, I 1931 I UNITED STATES PATENT orrlca LINN BRADLEY, ornon'rcraxn, NEW innsEY, AND EDWARD-.1. ucxnnrn, or NEW YORK, n. Y.,ASSIGNOBS 'ro BRADLEY mcxnnrn CORPORATION, A conropa'non or NEW Yoaxrnmmn'n'r or nnsnmn. mavens a i neauon mm January 14, 1924. Serial No.esa a'z.

This invention relates to improvements in the manufacture of pulp fromwood with a cooking liquor containing essentially sodium sulfite, eitheralone or admixed with caustic n improvedtmethod of pulp manufacture inwhich the pulp making operation is carried out with a cooking liquorcontaining essen- [tially normal sodium sulfite, either with or withoutthe addition of small amounts of 5 caustic soda. In ourprior applicationSerial No. ,535,034,' filed February 28, 1922, we have described anothermethod of pulp manufacture in which the cookin liquor employed is madeupessentially o caustic soda and 0 sodium sulfite, with the caustic sodain predominating amount.- In our prior apphcation Serial No; 665,224filed September 27, 1923 we have described still another method of pulpmanufacture in which the cooking l5 liquor is made up essentially ofsodium sulfite with excess sulfur dioxide, in excess of that requiredfor the normal sodiumsulfite.

The present invention relates to improve- 1 ments in the processes ofsaid prior applications, andparticularly inthe treatment of residualliquors from the, igestion or cooking operations of said processes, for\the regeneration of further amounts of cooking liquor for use in suchprocesses. According to the'present invention, the cpoking or digestionoperation and the regeneration or recovery operations may advantageouslybe. carried out in apparatus constructed and'intended for carrying. outthe sulfate process so-called. p I In the-sulfate process so-calledthe-cooking liquor consists essentially ofcaustic soda and sodiumsulfide; Varying amounts of, so-

diurmcarbohate, sodium sulfate, and other sodiumcompounds may also bepresent, but they are/generally considered to be, inert-in the process.Sodium sulfate or'nitre cake is I employed as the source of the sodiumsulfide, so and a considerable part of it is reducedto tion.

or which mayhereafter be pro ,SOdllllIl sulfide during thesmeltingopera- The sulfate process is recognized as having-certainobjections and limitations. The

residual liquor is diflicult to handle during the concentrating,calcining and smelting operations. Furthermore, the sulfate process isso objectionable in the malodors given ofi that sulfate pulp mills.should .be located away from centers of lar 'e population. Where locatedin' well popu ated territory, the resulting nuisance has been such thatcourt action has been successfully, invoked to prevent operation of theprocess.

The process of the present invention may utilize the lant and equipmentof existing sulfate mill 's, liquor as char line to litmus, ut it avoidsthe nuisance produced bythe objectionable odors of the sulfateprocess,'0r so greatly reduces the odors formed that it is accordinglywell adapted for use in-existing sulfate mills which are located nearcenters of population where operation of the sulfate process isrohibited, hibited; by court order; I

j the practice of the present invention, we may employ the digester ofthe sulfate- 'mill for carrying out the cooking operation,

provided it possesses sufiicient strength. We prefer-toemploy digesterscadpable of operating'at as high as 160 poun s pressure per' square inh, and where the cooking li nor is aid to -litmus tohave the digesterlined to protect the shell. We employ. as cooking liquor a solutioncontainingsessentially norespecially-when the cooking e into thedigesters is alka-j mal sodimn sulfite' (Na SOs) or sodium sul-'fite=and caustic soda, or sodium sulfite and excess sulfur dioxide. Bythe term excess sulfur dioxide? we mean the sulfur dioxide content overand above the amount required to form the normal The cook- I mg hquormay contain sodium sulfide and it may contain some thiosulfa'te;

or other sodium'sulfur compounds as well as other sodium compounds. Butwe-have found that where thiosulfa'te, or other sodium compounds whichcontain looselyhcombined sulfur, arelpresent in the cooking liquor,

objectionable odors are much less when the cooking liquor contains apreponderating amount of sodium sulfite than when such reagent isabsent. Especially when sodium thiosulfate is present in appreciableamount, sodium sulfite in amount sufficient to cook the wood overcomesthe objectionable features which the thiosulfate would produce if usedalone. Therefore in this invention the cooking of wood to produce pulpdoes not result in the formation of. the malodorouscompounds'characteristic of the sulfate process, or at least suchcompounds are formed in a less objectionable degree.

The residual liquors from the cooking 0peration, with neutralization offree acid content if any, may be treated, according to the presentinvention, in the evaporators, ro-.

.in'g out the improved process of the present invention with smallexpense for added equipment.

i The process of the present invention varies somewhat with thecomposition of the cooking liquor employed. These distinctions,

from the standpoint of the cooking operation, 7

are referred to in our prior applications in which these. respectiveprocesses are described. The cooking operations can be carried out withcooking liquors of varying compositions, and upon different kinds ofwoods, as pointed out in-said prior applications. 1

Insofar asthe pulp making operation itself is concerned, the process ofthe present invention presents the same advantages as the processes ofour said prior applications,

and is of more or less general application to woodsofvarious-kindsflncluding woods which'are not commonly regarded as pulpwoods at all. The present invention is thus appllicable not only to theusual pulp woods sue to short-fiber hard woods such for example as I.birches, beeches ;maples, etc. and also to other long fibered conifers,such as jack-pine, tamai'ack, loblollypine. hemlock. etc.

.-At the-end of the cooking or digestion operation, the residual liquorwill be ofa different composition and character from the residual liquorof the sulfate process. Some of the residual liquor may be usedover'again in making up the cooking liquor for a successive cook. Where densehard woods are employed',-the composition of the residual liquors willbe somewhat different than when as spruce and poplar, but is applicableconiferous woods such as for example jack pine, are used. It is oneadvantage of the process that the residual liquor may already econcentrated to a considerable degree in the sense that it mayicontainrelatively much more organic matter and much more sodiumcompounds perunit volume than the residual liquor from the sulfate process when thelatter isoperated exclusively with fresh liquor.

The residual liquor, according to the present invention, is subjected toevaporation, calcination and smelting, using evaporators, calciningfurnaces and smelters which may be. those of a sulfate mill. The processdoes not present the difficulties of concentration which the blackliquor from a sulfate mill presents,-

and the liquor can be concentrated to a high degree in multiple effectevaporators .b'efore introduction into the calcining furnaces;althoughthe residual liquor may in some cases be produced directly ofsuch a concentration that it can be fed directly to the calciningfurnaces.

From the calciners, the black ash may be charged into the smelter,together with additional carbonaceous material if necessary,

- and there subjected to a smelting operation,

This smelting operation is distinguished in important respects from thesmelting operation of the sulfate process. The black ash is easier tosmelt- The melt or smelt ob tained from the-smelter can be dissolvedinwater and treated for the production of further amounts of cookingliquor therefrom without the use of lime.

The operations thus far described may be carried out in the existingequipment of-a sulfate mill, although the operations differ in importantrespectsfrom the correspond-fing operations of the sulfate process. InparticulaL-the digestion, concentration, calcination and smeltingoperations are carried out with materials of a different character andwith less objectionable odors than-the sul- I fate process gives.

' In the sulfate process. smelter contains relativelylarge amounts ofsodium sulfide, and this sulfide is employed in the further carrying-outof the cooking process. In the process of the present invention.however, the melt from the smelter will usually contain onlv arelatively small amount of sodium sulfide. This amount may be so smallthat it canbe utilized in the cookprocess, in which case the cookingliquor will the melt from the inc," liquor in the further carrving outof the contain a small amount of sodium sulfide as I well as aprepon'deratinsz amount-of sodium sulfite, or of sodium 'sulfite andcaustic soda. It may also contain some sodium thiosulfate.

Where, however. the sodium sulfide is'not desired in thelcookine liquoror where the amount of sodium-sulfide in the melt is larger than isdesired in the cooking liquor, the solu-v tion of the melt may betreated for the conversion of the sodium sulfide into other compounds.The invention includes different methods of treatment of the solutionfor this purpose.

The addition of further amounts of sodium compounds to make up forlosses in the process may take place at different stages of the process.Salt cake or niter cake for example can be added to the desired extentto the little added equipment to that of a sulfate residual liquorbefore or after concentration and advantageously before calcination, or

after calcination and before smelting, and in.

such case, the added sodium sulfate .may be converted largely intosodium sulfide by the smelting operatiomso that the solution of the meltwill contain a correspondingly increased amount of sodium sulfide, whichmay be utilized in the cooking operation or which may be advantageouslyconverted into sodium sulfite or other compounds by suitable treatment..5

Instead ofadding sodium sulfate or niter cake or salt cake to supplyadded amounts of sodium, sodium carbonate may be employed and may beadded for example to the solution of the melt before it is subjected tofur ther treatment. A One way of treating the solution of the recoveredsodium compounds, after calcination and smelting, to convert sodiumsulfide into other sodium compounds of the kind described, is to subjectthe solution to treatment with carbon dioxide in such mannerthat acarbonate of sodium is formed. Hydrogen sulfide which is given off maybe burned to produce sulfur dioxide and this sulfur dioxide utilizedto'convert sodium carbonate into sodium sulfite. This hydrogen sulfidecan be regenerated containing essentially sodium sulfite or containingsodium sulfite and caustic soda. The regenerated solution can also,where desired, be admixed with residual liquor from the digesters inmaking up the proper volume and concentration of active chemicals to thedesired point for use in the further carrying out of the cookingoperation.

The process thus far described requires but mill. A small sulfur burner,a simple absorption tower, and conversion tanks for converting thesodium sulfide into other sodium compounds constitute most of the addedequipment necessary. The added reagents to make up for those lost in theprocess may be supplied by lime, sodium carbonate and the burning ofsulfur, or in part by niter cake or salt cake.

Where sodium bisulfarte is added to the residual liquor, this sodiumbisulfate will react with reactive sodium compounds to form normalsodium-sulfate. The solution containing sodium sulfate and other sodiumcompounds and organic matter may be evaporated and calcined in otherapparatus than the vacuum evaporators and rotary kilns. For example, theliquor may be. subjected to spray'evaporation with hot gasesor-otherwise, and the resulting dried product then subjected to thesmelting operation. Where the liquor itself does not contain sufficientreducing materials (e. g. carbon from decomposition), further amounts ofcarbonaceous materials may be added so that the sodium sulfate will belargely reduced to sodiumsulfide, and so that the melt may containsodium carbonate and sodium sulfide y be burned n the combustion ctogether with some sodium sl11fite,'sodium of a sulfur burner and thusmixed with sulfur dioxide gas resulting -from the combustion of sulfur,and this sulfur dioxide can be used for treating the solution containingthe I sodium carbonate to convert the carbonate to the desired extentinto sodium sulfite..

The liquor maybe treated to free it from sodium sulfide, where suchtreatment is desired, and thentreated with lime to convert the greaterportion of the contained sodium carbonate into caustic soda, care beingtaken that the sodium sulfite that may be contained in the-liquor is notconverted to any large extent into caustic soda. The causticized liquorwill then contain caustic soda together 1 with more orless'sodiumsulfit'e', and it may also contain varying amounts ofsodium-carbonate, sodiumsulfate, sodium thiosulfate, etc. Thecomposition of the liquor can be regulated for example by add ng sodiumcarbonate before causticizing where the. amount of caustic'soda is to beincreased, or by adding further amounts of sodium sulfite, or" by forminfurther amounts ofsodium sulfite in the sulfate and other compounds.

The incineration or calcination of the dried residual liquor results inthe destructive dIS- tillation of the material and the formation ofvaluable products which may be passed through a condenser tocondense'combustile liquids such as alcohols, acetone, etc. Such',-

liquor can be utilized by blending with other 2 ingredients such asgasoline,-3;lcohol, benzene, acetylene, etc. for making mdtor fuel orother fuel compositions; The non-condensible lid gases from theincineration or destructive distillation. can be utilized as fuel, :forex-- ample, in drying'or evaporating the residual iquor.

considerable amount of sodiumsulfide or When the solution of the meltcontains a the treatment of this solution directly with sulfur dioxidegas will set free carbondioxide and cause more or less of the sodiumsulfide and polysulfides to be converted into sodium thiosulfate '(uasmn. If-= the solu'-" tion contains a fairlyahighj percentage of.

quor. In this way a cooking liquor? sulfidef or polys ulfides,this'fiirect treatment of the solution with sulfur dioxide will resultin a solution containing a high proportion of thiosulfate. Ac ording tothe process of another invention of ours we take advantage of l thisformation of thiosulfate in producing a cooking liquor for cooking broadleaved or deciduous Woods to produce a special kind of pulp therefrom.We have found that the use of such a cooking liquor, consistingprimarily ofthiosulfate, is of advantage as applied to broad-leaved ordeciduous woods for producing certain kinds of special pulp, and thatthe residual liquor from such pulp making operations can. be treated forthe recovery of the thiosulfate for further use in the cookingoperation. This thiosulfate process, however, forms the subject of aseparate application and we do not claim the same herein. Where it isdesired to obtain wood pulp suitable for bleaching, we have 'found thatI it'is desirable to avoidthe presence of a proportionally large amountof thiosulfate in the cooking liquor, and that it is desirable to treatthe residual liquors so that the cook-' ing liquor obtained therefromwill contain a proportionally large amount of sodium sulfite. By usingsuflicient sodium sulfite in the cooking liquor, and only a relativelysmall amount of thiosulfate, or no thiosulfate at all, the formation ofdark pulp diflicult to bleach is prevented. 'If the amount of sodiumsulfite in the cooking .liquor is equal toaround 30 to of the bone dryweight of the wood, a considerable amount of thiosulfate may'becontained in the cooking liquoranda readily bleach'able pulpnevertheless obtained. i

Wherefthe residual liquor from such a cooking operation, in which somesodium thiosulfate is used, is evaporated,- calcined in the presence ofair, and subsequently smelteduthe thiosulfate undergoes decompositionand some sulfur is eliminated froni the cycle, so that therecoveredchemicals can be treated for the production of cooking liquorof suitable composition without. objectionable upbuilding' ofthiosulfate in the cooking liquor.

By suitable. treatment of the solution of the melt, the formation ofsodium thiosulfate from the sodium'sulfide of the solution can besubstantially prevented. -For this purpose, the solution canadvantageously be treated first withcarbon dioxide to convert the sodiumsulfide into. carbonate or bicar-- bonate-and liberate hydrogen sulfide.Carbon dioxide gas, preferably in highly-concentrated condition, maythus be passed into an absorption tower or tank containing the solutionof the melt. .By decomposing the sulfides in this way and removing thehydrogen sulfide liberated, the formation of thiosulfate upon subsequenttreatment of the solution with sulfur dioxide, is substantially avoided.By using relatively pure and conccntrated carbon dioxide and a suitabletower or tank, a nearly pure and concentrated hydrogen sulfide gas isdriven off from the top of the tower or tank. This hydrogen sulfide gas,accompanied by any unabsorbed carbondioxide, can then be burned, forexample, by introducing it into the combustion chamber of a sulfurburner, thereby burning the hydrogen sulfide to-sulfur d1- oxide andWater. formed will admix with that from the sulfur burner and can beemployed in the manufacture of sodium sulfite.

' The sulfur dioxide from the sulfur burner, together with'the addedsulfur dioxide from the combustion of the hydrogen sulfide, may

be absorbed in an absorption tower or tank ina solution of sodiumsulfite which gradual- .ly increases in freeacid content. Thetemperature and'the percentage of free and combined sulfur dioxide canbe controlled at Wlll.

By regulating the concentration and rate of The sulfur dioxide thusadmixture thereof, with thorough agitation,

and with the resulting setting free of carbon dioxide and the: formationof a correspond ing amount ofsodium sulfite. This nearly pure carbondioxide gas, or as much of it as necessary, can be used intreating thesolu tion of the melt for converting the sodium sulfide into sodiumcarbonate and driving off hydrogen sulfide. The resulting solution,which may be substantially free-from sodium sulfide, and containing acorresponding in-I creased content .of, carbon dioxide, may be thesolution to which the acid sulfite solution is added as above described.WVhen the process is thus carried out, carbon dioxide may be usedrepeatedly and successively in reacting with the sodium sulfide to formdiumcarbonate which is later decomposed wit fite.

The carbonated solution from. the carbonating tower or tank, after theconversion of sodium sulfide into sodium carbonate is divided insuchproportion as needed, part going to the sulfur dioxide absorptiontower.

or tank and part going to make up the cookingliquor for the cooking"operation. Where the cooking liquor is to contain essentially sodiumsulfite (Naso with only small the acid sulfitesolution to drive off thecarbon, dipxide again and formsodium sulamounts of other sodium salts orof caustic soda, the carbonated solution from the car bonating tower ortank may be neutralized with the acid sodium sulfite solution from thesulfur dioxide absorption tower or tank tion employed in making up thecooking hquor.

and a su-flicient amount of the resulting solu- 1 Where the cookingliquor is to contain both sodium sulfite and caustic soda, at part ofthe sodium carbonate may be treated with lime and subjected toaregulatedcausticizing operation, and the proportions of caustic soda and sodiumsulfite may be varied as desired.

It will be evident that where a cooking liquor which is acid incharacter is desired,

for examplega'booking liquor containing an;

amount of sulfur dioxide greater than that corresponding to sodiumsulfite and less than that cprresponding to sodium, bisulfite, theresidual liquor can be subjected to a similar concentration, drying,calcining and smelting operation, and the solution'of the melt can betreated in the manner above described, and the solutions so produced canbe so combined that a cooking liquor containin the desired amounts ,ofsulfur dioxide both res and combined can be obtained. Where forexamplean acid sodium sulfite cooking liquor is dean acid-proof liningmaybe required in the digester during the cooking operation,particularly where a large excess. of sulfur dioxide is present. If theamount-of excess sulfur dioxide is sufiiciently small, an' acidprooflining maybe unnecessary. The di-' gester, when operated at higherpressures "than those commonly employed in the sulfate process, shouldof course .be of a stronger or; reinforced construction which will useof the high pressures desired.

The residual liquors from such an acid sul fite process in which anexcess'of sulfur dioxide is used over and above that required for thenormal sodium sulfite can be treated In a 811111131 manner to that abovedescribed,

' tus;

making use of the existing equipment of asulfate m1ll ,.or using othersuitable appara- A flow sheet illustrating the recovery process abovedescribed is shown conventionally in the accompanying drawin Theresidual liquor from the digester is su bjected to evaporation inevaporators and then to incineration in incinerators, and to smelting,and the smelted product is then dissolved in dissolving tanks. "theapparatus "used in these operations mayb'e those'of the sulfate process,

as above described.

containing sodium carbonate and varying amounts of sodium sulfide,depending upon the composition of the residual liquor treated and themethod of'incineration, passes to one or the other'of thetwo stora etanks indicated on the flowsheet as 2 circulating tanks. Fi'om one orthe other of these tanks the solution is circulated through the carbo-'GO tower. In this tower the solution is subjected to the action ofcarbon dioxide which acts upon the sodium sulfide to form ,a carbonateof sodium and to set free hydrogen sulfide. The hydro en sulfidetogetherwith any unabsorbed carbon'dioxide may be conveyed to the.combustion chamber of the sulfur burner where the hydrogen sulfide isburned to form sulfur dioxideand water vaporsufliciently carbonated itis pumped to one or the other of the two adjusting tanks where it issubjected to treatment with a solution of sodium bisulfite, or asolution of sodium sulfite containing a greater or smaller amount of SOthan corresponds to sodium bisulfite, preferably with introduction ofthe bisulfite solution at the bottom,.and'with gentle agitation. Theaction of this sodium bisulfite solution upon the sodium carbonatesolution is to set free carbon dioxide in a relatively pure andconcentrated state. The carbon dinating tower referred to on the-blueprint as,

When one of the tanks of liquor has been From the dissolving tanks, theliquor oxide may be collected in a gasometer from Which a sufficientamount is supplied to the carbonating tower or tank' while the surpluscarbondioxid'e can be passed to a compressor or otherwise utilized. q

When one of the adjusting tanks has'been neutralized and the carbonatedecomposed the resulting solution of normal sodium 'sulfite can be inpart conveyed to the digesters for use asamake-up liquor for furthercookingoperations, or its composition canbe modi fied .to give a cookingliquor of either acid or alkaline'character'. The remainder of th'sodium sulfite solution from the adjusting ank may be conveyedto one orthe other of the sulfur dioxide circulating tanks from which it"is'circulated through the sulfur dioxide aabsorption towerortan-k to absorba sulfur dioxide from the sulfur burner. By passing the hot gases fromthe sulfur burner-through the absorption tower down which the sodiumsulfite solution passes, the solution gradually increases intemperature, and in excess sulfur dioxide conteiit. By regulating theconcen-' tration and rate of flowof liquor and gas, the

'- amount of sulfur dioxide absorbed can be regulated and controlleduntil a solution corresponding to sodium. bisulfite, or with greater'orless sulfur dioxide contant" is obtained. The percentage of sulfurdioxide,

tion.

absorbed can be controlled at will. This sodium bisulfite liquor canthen be returned to one of the adjusting-tanks or it can be in partemployed in further cooking opera- 1 The sulfur dioxide from the sulfurburner together with the sulfur dioxide formed from the hydrogen sulfideis absorbed in the S0 tower or tank while the .inert gases (nitro-'genand carbon dioxide) escape to the atmosphere. The process of the flowsheet as described and illustrated is a self contained process in Iwhich the only addedreagent is sulfur for v p v the sulfur burner tosupply additional sulfur dioxide; while the regenerative process gives asolution of either normal sodium sulfite or of sodium-bisulfite orliquors of intermediate composition which can be used as such or furthermodified in the carrying out of the proc ess. Carbon dioxide may beobtained as'a by-product. Additional sodium to make up for losses in theprocess can be supplied in various ways. Sodaash or sodium carbonate canbe added at any point prior to the treatment of the solution of odiumcarbonate with theacid sodium sulfite solution. Sodium sulfate or nitercake, if used, should be added before the incineration so that it willbe in 3 part reduced to sodium sulfide during the smelting operation."The. sodium sulfide so produced may be utilized for the formation ofsodium carbonate, and the hydrogen sulfide given ofi may be recoveredand can be' 35 recombined after oxidation to SO with the sodiumcarbonate solution to'giv sodium sulfite and set free carbon dioxide.

The recovery process above described is itself a new recovery processfor the treatment of residual li uors of the character tion of thecalcined or incinerated product hereinbefore referre to for theproduction therefrom of further amounts ofcookingliqs uors. It is ofspecial value and application where sodium sulfide is resent inthe-soluand where sodium sulfide" is not desired,'or

" where a considrable reduction of the amount of sodium sulfide isdesired, in a cooking li uo'r.

'e process makes possible the elimination of the sulfide byconverting itinto sodium carbonateand hydrogen sulfide,

while, the hydrogen-sulfide may. be burned to sulfur dioxide for furtheruse in the process. In this way the objections incident to the presenceof sulfide in -the cooking operation are overcome; -while the processneverthel'ms makes posible theuse ofw sulfatelor nifer. cake as a sourceof additional sodium compounds in the bon dioxide'toform of sodium"iFi'a 'm the process may eonthe umv'ersionbf sulfide, the decomofthe'aodium sulfide with car:-

further carbonatin operations, p

7 Other methods 0 decomposing the sodium sulfide or 'polysulfides andremoving them from a solution of the melt can also be emformation ofsodium carformed by treating the sodium carbonate s o-' lution withsodium bisulfite will be'in excess of that required for convertingsodium sul 1 fide into sodium carbonate. Apart of this excess carbondioxide may be used to convert sodium carbonate into sodium bicarbonatewhich may be precipitated in the carbonating tower or tank and recoveredtherefrom. v The introduction of carbon dioxide into the solution' ofsodium carbonate and sodium sulfide may take placein an absorption towerwith baflles 'or other filling material or obstructions to insureadequate absorption and reaction, orv carbon dioxide can be introducedthrough a porous bottom, e. g., filtros bottom,

into a tank of suificient de th to insure adequate absorption of the car11 dioxide in the li uor. I

nstead of using difierent a 'paratus for the carbonating' operation anthe sulfur dioxide absorption operation, these opera tions canadvantageously be combined by'using'a deep tank of small cross sectionand in through a porous medium suchas filtros plates. By introducingsulfur dioxide in this manner into a solution containing sodiumcarbonate and sodium sulfide, sodium troducing thesulfur dioxide at thebottom 1 sulfide will be deeomposed and hydrogen sul fide driven ofi,while the sulfur dioxide will react upon the 'sodium'carbonatein thelower part of the tank, setting free carbon dioxide which in itsupwardpassage will react with the sodium sulfide to set. free. hydrogensulfide. When operating in this way main portion of carbon dioxide willbe subsequently removed. The hydro en sulfide can beutilized as abovedescribe while the carbon dioxide can similarly be employed for ployed,although we considerfthe cycli'c process above escribed' as particularlyadvantageousf Where only small amounts of "sulfide are present, they maybe removed for example by adding iron sulfate, with resultthe hy- F V'drogen sulfide will-be driven off first with a limited amount of carbondioxide and the.

precipitation of iron sulfide. Where ium carbonate, is present, calciumsulfate.

can be added to remove the carbon dioxide as calcium carbonate, leavingsodium sulfate in dium sulfite with excess sulfur dioxide.

We have further found that when residual liquors of the characterreferred to are subjected to calcination without smelting, the solutionor extract obtained from the calcined Further amounts of cooking liquorstherefrom, or a part of the residual liquor can be returnedwithouttreatment for use in making up the charge for further cookingoperations, in which case the cooking liquor will be a mixtureofresidual liquor and fresh sodium sulfite liquor which 'may be thatobtained by the regenerat ve process. I The residual liquor from thle;cooking process in which sodium sulfite and causticsoda are employed,or1from the process in which sodium sulfite'and excess sulfur dioxideare employed, can similarly be treated product may contain small amountsof so-j directly forthe recovery of fresh cooking dium sulfide orpolysulfides, particularly where the calcination is carried out underreducing conditions; and that the solutions so obtained canadvantageously be treated in .the same manner as solutions of smeltedproducts for the removal of sulfides therefrom. Thus, in case theresidual liquor is evaporated and calcined or carbonized under reducingconditions, and then leached to extract the soluble salts therefrom, anda solution obtained which contains sodium sulfide,

this solution can be treated first to convert the sodium sulfide intoother compounds, in much the same manner that solutions of the smeltedproduct are treated for the conversion of the sodium sulfide into otherproducts.

The invention will be further illustrated by the following specificexamples.

Woods of varying kinds, such as spruce,.x

and insuring a thorough penetrationof the chips with the 'cookingliquorduringthe preliminary portion of the heating operation,

(preferably below 110 C.) the digester can,

subsequently be heated to a higher temperature and pressure without.objectionable action upon the chips, and with substantially completecooking of the chips even when long fibered resinous woods are employed.The

cooking operation carrbe carried out as a single stage operation, on nsuccessive stages,

a and, where two stages are employed, a different cooking liquor canb'eused in the second stage. When a normal sodiumsulfite 'cgoking liquor isused. in the first stage, sodium sulfide. may be present in the secondstage with less objections than are incident to. it use in tSulfatepro'cess. \l l The residual liquor from the normal sodium sulfitecooks above meat-erred to can be directly treated forthe recovery offresh liquors therefrom or a part of the residual liquor can be returnedwithout'treatment for use in making up the charge of further cool;- ingoperations, in which case the cooking liquor will be of a compositecharacter, being made up in part of residual liquor and in part of freshcooking liquor obtained by the regenerative process of the presentinvention By returning part ofthe residual liquor and reusing it, thecontent of the residual liquor in organic material and inorganicconstituents can be built up so thata more concentrated liquor isavailable for further treatment in the. regeneration process and weclaim such operations as part 0 our invention.

The residual liquor may be evaporated in amultiple effect evaporatorsuch as a triple effect Yaryan evaporator to about 36 to 38 B.. and thenrun through a rotary furnace and converted into a product which may bereferred to as reen ash. This green ash may then be fed m-to the.preheated smelter and burned and s'melted to form a free run- 'nin meltwhich is conveyed to the dissolving tan The green ash was found tocontain a s'uflicient amount of organic matter to burn readily withoutadditional fuel, and the burning and melting operations appear moreadvantageous than those of'the sulfate rocess. The calcination oftheconcentrate liquor in rotary furnacesaalso appeared to take place withless flame appears in the sulate process, so; that"a;*g'reaterpercentage of total .heat units isretamd in the green ash when discharthe rotary "to be charged into t 'e ainelter.; The ease of burningof'the ash and th ow melting point of the smelted product as foimd toenable the smelting operation placein a particularlyadvantageousfifiannerf When the liquorin thetank,

into which the hotjrnelt. was received had reached a density: of about26"" B6, hot the liquor was found on analysisto contain considerable'carbonate, some sulfides "and a conslderable amount of sulfite. Whenthis liquor was treated: with hydrochloric acid. considerable' sulfurwas thrown" out of solution. When treated with sodium bisulfite Solutionhttle sulfur was thrown out of solution, al-

though the liquor was made acid to phenolphthalein. r

I Instead of using fresh water or wash water to dissolve the melt, or toleach the calcined unsmelted product, the residual liquor fromtheprocess'can be used for this purpose, thus building up the strength ofthe liquor and I saving in evaporation. Where the residual liquorcontains considerable unconsumed sodium sulfite, thisexcess ofreagentwill-be made availablein further cooking operations. By dissolving themelt-in the fresh residual liquor, and by then removing the somewhat dihydrogen sulfide and so treating the result: ing solution with sulfurdioxide. as to convert the carbonate into sulfite, and by clarifying ifnecessary to remove precipitated material, etc., a suitably concentratedcooking liquor can be obtained well adapted for reuse in the cookingstep of.the process.

Instead of treating residual liquors from the normal sodium sulfitecooking process, the residual liquor from the process in which causticsoda and sodium sulfite are employed can betreated in a similar way. Inthis case,

however, the residual liquor will be of a rent composition, and, inorder to regene te a similar cooking liquor,

- causticizing of some of the sodium carbonate with lime can replace theconversion of acorresponding amount of sodium carbonate to sodiumsulfites may be used, and the residual liquor by evaporation,calcination, smelting and dissolving, can be carried out in a similarmanner to that above described with the normal sodium sulfite residualliquors. To the extent that the resulting solution of the melt is ruired to be converted into sodium sulfite, snnilar methods tdthose abovedescribed can be used, supplemented by causticizing of part ofthe-liquor with lime to convert sodium carbonate into caustic soda.

Residual liquors from the pulp making 1 process in which acid sodiumsulfite, or sodium sufite with excess sulfur dioxide (as hereinbeforedefined), are used, can also be treated in-a somewhat similar way forthe regeneration of cooking. liquor therefrom In ,this case, however,the residual liquor will beef :1 somewhat difierentcomposition and thetreatment may be modified.v The acid character of the residual liquor,and the increased'content of sulfur dioxide in proportion to the sodiumcontent tends'to cause an increased amount of the sulfurdioxide to begiven off duringthe concentrating, calcining and smelting operations..Ihis sulfur di-- oxide can be recovered, however, e. g., by absor tionand returnedgto the process. .The

' residual liquor can also be advantageously treated to neutralize itbefore it subjected to the concentrating, carbonizing and smelt-' ingoperation.- For this purpose the solution of the; melt, or the partiallycaustici'zed 05 solution of the melt, may be used.'- By adds ing thedesired amount of the melt directly.

to such a residual liquor, the liquor will serve to dissolve the meltand will be preheated and neutralized to a greater or less extent at thesame time. The neutralized residual liquor, neutralized in this orsomeother suitable manner, may then be subjected to evaporation,

process itself, in the manner hereinbefore refrredto.

It will thus tion provides improved methods of-regen-' crating theresidual liquors from processes in which normal sodium sulfite, orsodium sulfite and caustic soda, or sodium sulfite and sodium'bisulfite, or sodium sulfite and sul be seen that the presentinvenfurous acid, etc. are employedffor the production of furtheramountsof cooking liquor therefrom; and that theoperations can inthiswaybe. improved and regulated and controlled in a particularlyadvantageous manner. Among the various features of advantage which theinvention presents, as hereinbefore described, are included thereutilization of re"idual liquor itself in further cooking operationseither with or without admixthe recovery of the chemicals contained inthe residual liquor by various methods of procedure whereby theyare-made available.

ture of fresh amounts of reagents thereto;

for furthericooking operations; the evaporation of'the residual liquors,carbonization and smelting, and dissolving of the melt with subsequenttreatment of the resulting solution for the regeneration of cookingliquor therefrom; the carbonizationof the concentrated residual liquorwithout excessive reduction and resulting recovery from the;carbonize dproduct of soda for further use in the process the utilization ofexisting equipment of sulfate mills with a moderate amount of'ehange funand expense, and'with advantages hereinbefore described, and withavoidance of certain objections incident to the sulfateprocess itself;the'utilization of sodium sulfate or 'niter cake in supplyingadditionalchemicals f to the. pr0cess, with elimination of sulfide. radical ifdesired and utilizatiouof the sulfur content thereof in the furthercarrying on -'of the process; 'the treatment of solutionscolitainingvsodium sulfide to'remove sulfur therefrom and convert thesodium. intoso 'dium sulfite, with utilization of the hydrogen sulfidegivenoiflfor producing sulfur dioxide by combustion; and various'otherfeatures of improvement hereinbefore described.

The improvements of the present invention supplement the improvements ofour prior applications and are of value in connection with manufactureof pulp and paper from woods of various kinds, including not only woodscommonly considered as pulp woods such as spruce and poplar, but alsowoods which are not commonly considered as pulpwoods at all, or woodswhich are considered of. little value for pulp making purposes, such asthe heavy hard woods (birches, beeches, maples, oaks, gums, etc.) andresinous coniferous or long fibered woods such as ack-pine, loblollypine, tamarack, etc.

While the invention has been described more particularly in connectionwith the use of sulfites of sodium, yet it will be understood thatsulfite's of potassium or mixtures of sulfites ofsodium and potassiumcan be similarly used; and that sulfites of magnesium can to some extentlikewise be used, although we consider the use of sodium sulfites asparticularly advantageous. Sulfites' of potassium will ordinarily be tooexpensive for commercial use,although they-may be used where cheapdeposits containing suitable potassium compounds are available.Similarly, mixtures of .magnesium and sodium sulfites maybe used, andthe residual liquors from their use treated for the regeneration offurther amounts of-cooking liquor therefrom.v V Magnesium sulfate,either alone or accompanied'by'sodium sulfate, may be added to asolution of'the melt to convert the sodium carbonate into sodium sulfateand the magnesium sulfate into magnesium carbonate. 40 ,The sodiumsulfide may-be eliminated by precipitation or by volatilization of thesulfide radicle. For example, iron sulfate can be used for precipitationof iron sulfide, or sulfuric acid, nitre cake, or CO may be used todrive off l-LS. The sodium sulfate solution can then be treated withGaSO and H 80 to form Ca'SO 2H O and leave an acid solution containingsodium sulfite.' Other solu ble metallic salts may be used toprecipitate insoluble metallic sulfides, e. g. copper sulfate.. a Weclaim: 1. In the treatment of residual liquors from pulp-makingoperations in which an alkali metal sulfite is employed in the cookingliquor, the improvement which comprises evaporatin such liquors,subjecting the residue to calcination, smelting the calcined product,dissolving the result'fiig melt and .60 treating the solution todecompose sulfide contained therein.

21- In the treatment ofresidual liquors from,.pulp-making operations inwhich an alkali 'metal sulfite is employedin the cooking liquor, theimprovement which comprises evaporating such liquor, subjecting theresidue to calcination, smelting the calcined product, dissolving theresulting melt and treating the solution to decompose sulfide containedtherein, said treatment including the treatment of the solution withcarbon dioxide to convert sulfide into a carbonate and to drive offhydrogen sulfide.

3. In the treatment of residual liquors.

from pulp-making operations in which an alkali metal sulfite is employedin the cooking liquor, the improvement which comprises subjecting suchresidual liquors to evaporation, subjecting the residue to calcination,and subjecting the calcined product to a smelting operation.

4. In the treatment of residual liquors' I the resulting solutiontreated for the production of further amounts of cooking liquortherefrom.

' 7. The further improvement in the process of claim 4in which the meltis dissolved in a portion of the residual liquor and the resultingsolution treated for the production of further amounts ofcooking liquortherefrom. I

8. The improvement in the process of claim 4 in which the melt isdissolved to form a solution, the solution treated with carbonic acidradical to decompose sodium sulfide and drive off hydrogen sulfide, thehydrogen sulfideburned to sulfur dioxideand sulfur di-.'

oxide absorbed in the solution from which the hydrogen sulfide hasbeendriven off.

9. The improvement in the process of claim 4 whieh 'c'omprisesdissolving the melt to form a solution thereof, treating the solutionwith carbon dioxide to decompose sodium 'sulfide and drive off hydrogensulfide, burning'the hydrogen sulfide and some sulfur for the productionof sulfur dioxide, and treating the solution of the melt from which thehydrogen sulfide has been driven off with sulfurous-- acid radical toconvert the carbonate into a sulfite. a y 10. The improvement in thetreatment of residual liquors from pulp-making operations in which .asulfite of sodium is employed in the cooking liquor, which comprisesevaporating the. residual liquor, calcining and smelting the residualmaterial, dissolving the melt to form a solutionthereof, treatingsolution containing sodium carbonate and so-.

the solution with carbon dioxide to decomse sodium sulfide and drive ofihydrogen sulfide, treating the resulting solution with an acid sulfitesolution containing suificient sulfur dioxide to convert the carbonateto sulfite, burning sulfur and the hydrogen sulfide to-form sulfurdioxide, absorbing sulfur dioxide to form a further amount ofacidsulfite solution, and employing such acid sulfite solution for treatingthe solution of the melt in the earlier step of the process.

11. The improvement in the claim 10 in which additional sulfate ofsodium is added prior to the smelting operation, thereby giving anincreased amount of sodium compounds in the solution of the melt and anincreased amount of sodium sulfide and of hydrogen sulfide in theprocess.

12. The method of producmg solutions containing sddium sulfite from asodium sulfate which comprises reducing sodium sulfate to sodiumsulfide, treating a solution containing the sodium sulfide with carbondioxide to form a sodium carbonate and hydrogen sulfide, and absorbingsulfur dioxide in the sodium carbonate solution to form sodium sulfite.v

13. in the treatment of residual liquors from pulp-making operations inwhich a sulfite ofsodium is employed, andin which the residual liquor isconcentrated, the residue calcined and the product leached to form adium sulfide, the step which comprises treating such solution withcarbon dioxide to conv vert thelsulfide into carbonate and set freehydrogen sulfide, and the further ste which comprises treating thesolution so 0 tained with the sulfurous acid radical to convertcarbonate into sulfite.

14. The cyclic process of forming solutions containing sodium sulfitefrom solutions containing sodium carbonate, which comprises treatingsuch carbonate solutions with acid sodium sulfite to convert thecarbonate into sulfite, absorbing sulfur dioxide in part or all of thesulfite solution so formed, and treating a fulrther amount of carbonatesolution therewit 15. The cyclic process of forming solutions containingsodium sulfite from solutions containing sodium carbonate and sodiumsulfide,

" which comprises subjecting such solutions to treatment-withcarbondioxide to convert sulfide into carbonate and'set free hfydrogen sulsfide, burning the hydrogen sul de together with some sulfur to formsulfur dioxide, ab:

. sorbing the sulfur dioxide in the carbnoate solution to set freecarbon dioxide, and usingv the carbon dioxide in the further carryingout of the carbonatingstep of the process for -converting-sulfide"intocarbonate.

16. The cyclic process of'forming solutions containing sodium sulfitefrom solutions contaming sodium carbonate and sodium sulfide,

taining sodium sulfide and sodium carbonate,

fite solution to convert the carbonate into sulfite, and using thecarbon dioxide set free for the further carrying out of thecarbonatingstep of the process.

17. In the treatment of residual liquors from the cooking ofcellulose-bearing material with a cooking liquor containing sodiumsulfite, which residual liquors have been cons centrated and the residuecalcined, and the product treated to form a solution containing sodiumsalts, the step which comprises treat ingsuch solution with carbondioxide and subsequently with sulfur dioxide.

18. In the treatment of residual liquors from pulp-making operations inwhich a sulfite of a strong base is employed in the cooking liquor, theimprovement which comprises evaporating such liquors, subjecting theresidue to calcination, smelting the calcined prod: uct, dissolving themelt in a portion of the residual liquor and treating the resulting solution for the production of further amounts of cooking liquortherefrom.

'19. The method of treating solutions containing sodium sulfide andsodium carbonate, which comprises treating such solution with carbondioxide to decompose sulfide of sodium and form sodium carbonate inwhich a relatively purecarbon dioxide is used to treat the solution,thereby giving hydrogen sulfide, burning the hydrogen sulfide to formsulfur dioxide and absorbing sulfur dioxide in the solution.

20. The method'of treatingsolutions containing sodium sulfideand sodium.carbonate, which comprises treating such solution with carbon. dioxideto decompose sulfide of sodium and form sodium carbonate, burning "the.hydrogen sulfide and some sulfur to form sulfur dioxide, absorbingsulfur dioxide in a solution containing sodium sulfite, to give an acidsolution of sodium sulfite, and treating the solution containing sodiumcarbonate with such acid sulfite solution.

21. The method of treating solutions conwhich comprises treating suchsolution with 123 carbon dioxide to decompose sulfide of sodium andformsodium carbonate, burning the hydrogen sulfide and some sulfur toform sulfur dioxide, absorbing sulfur dioxide in a. solution containingsodium sulfite, to give an acld solution of sodium sulfite, and treat-'ing the solution containing sodium carbonate with such acid sulfitesolution in which the carbon dioxide obtained in a relatively pure andconcentrated state is used tothe req ir 130 extent to treat the solutioncontaining sodium sulfide and sodium carbonate to decompose sodiumsulfide and set free hydrogen sulfide therefrom.

22. The method of treating solutions containing sodium sulfide andsodium carbonate,

which comprises treating such solution with carbon dioxide to decomposesulfide of so-.'

, and form sodium carbonate, treating the carand bonate solution, afterthe removal of hydrogen sulfide, with an acid-solution of sodium sulfitecontaining an excess of sulfur dioxide, thereby obtaining a solution. ofsodium sulfite for use in further cooking operation.

24. The method of treating solutions containing sodium sulfide andsodium carbonate, which comprises treating such solution with carbondioxide to decompose sulfide ofsodium form sodium carbonate, treatingthe carbonated solution, after drivingoff hydrogen sulfide, with an acidsolution of sodium sulfite containing excess sulfur dioxide to convertthe carbonate into a sulfite, absorbing sulfur dioxide in the resultingsodium sulfite solution or in a portion of it and thereby forming afurther amount of acid sulfite solution, and'treating further amounts ofcarbonated solution with such acid solution.

25 A cyclic process which comprises digestmg raw cellulosic material ina sulphuro us acid solution of a soluble alkali or alkal ne earthsulphite, neutralizing the spent liquor resulting from such digestion,separating the pulp from such neutralized spent liquor, burning thecombustible content and smelting the inorganic mineral content of suchspent liquor in a reducing atmosphere in a manner to produce sulphideand carbonate, recoverlng the inorganic smelt in water, carbonatingthesmelt solution, and acidifying the carbonated solution with sulphurdioxide 1' uor.

6. A cycl-icprocess Jvhich comprises digesting raw cellulosic materialin a sulphurous acid solution of a soluble alkali or alkaline earthsulphite, neutralizing the spent liquor resulting from such digestion,separating the pulp from such neutralized and spent liquor, burning thecombustible and smelting inorganic material content "of such liquor in areducing atmosphere in a mannor to produce sulphide and carbonate,recovering-the inorganic smelt in water, car-.

bonating the smelt solution, employing a porproduce fresh acid digestingtion of such carbonate solution together with cyclic make-up compoundsfor such neutralization, and acidifying the remainder of thecarbonated-solution with sulphur (dioxide in a manner to produce a freshacid digesting liquor.

- 27. A process which comprises concentrating and burning thecombustible content and smelting the inorganic content of spent liquorresulting from the digestion of raw eel-- lulosic material in asulhurous acid solution of soluble alkali su phite or alkaline earthsulphite, in a manner to produce substantially only sulphide andcarbonate, re-- covering the smelted inorganic compounds in water,carbonating the smelt solution with substantially pure carbon dioxideand conlulosic material in a sulphurous acid solution of soluble alkalisulphite or alkaline earth sulphite, in a manner to producesubstantially only sulphide and carbonate, recovering the .smeltedinorganic compounds in water, carbonating the smelt solution withsubstantially pure carbon dioxide and controlling such carbonation toproduce a substantially pure hydrogen sulphide, acidifying thecarbonated solution with a substantially pure sulphur dioxide,controlling such acidification to produce a substantially pure carbondioxide, and utilizing 'such' carbon dioxide in the carbonation of othersmelt solution.

29. A- process which comprises concentrating and burning the combustiblecontent and smelting the inorganic content of spent liquor resultingfrom the digestion of raw ce1-.

lulosicmaterial ina sulphurous acid solution of a soluble alkali andalkaline earth sulphite, in a reducing atmosphere in a manner to producesubstantially, only, sulphide \and carbonate, recovering the smeltedinorganic compounds in water, carbonating the smelt solution, oxidizingany remaining sul-.

phide, and acidifying the carbonated soluas is needed to produce a freshacid digesting liquor.

30. A process which comprises digestin raw cellulosic material in asulphurous acid solution of a, soluble alkali sulphiteor alkaline earthsulphite, concentrating and burning the combustible content and.smelting tion with sulphur dioxide in such amount the inorganic 'conteg;

'32. A process which comprises raw cellulosic material in a sulphurousacid of spent liquor resulting from such estion in amanner .to produce,sulphide and carbonate, recovering the smelted inorganic compounds inwater, 5 carbonating the smelt solutn with carbon dioxide andcontrolling such carbonation to produce hydrogen sulphide and to effecta conversion of substantially all the sulphide to carbonate, burningsuch hydrogen sulphide to produce sulphur dioxide, recovering thegaseousproducts of combustion, acidifying the carbonatedsolution withsulphur dioxide and controlling such acidification to produce asubstantially pure carbon dioxide and a sulphite solution, utilizing thecarbon di- 'oxide obtained in such-acidification for the carbonation ofother smelt solution, and utilizing said products of-combustion in theproduction of a sulphite cooking liquor.

- line earth sulphite, concentrating and burning the combustible contentand smelting the inorganic content of spent liquor resulting to produce-phide, and recovering the latter in an aqueous such solution withcarfrom such digestion in a manner sulphide and carbonate, recoveringthe smelt- .ed inorganic compounds in water, carbonatdioxide, burningthe hydrogen sulphide resulting from such carbonation and recovering thesulphur dioxide thereby produced,

acid iifying the carbonated solution with dibustionof'the hydrogensulphide in the production of fresh cooking liquor.- a digestingsolution of a soluble'alkali sulphite or alkaline earth sulphite,concentrating and burning the combustible content and smelting theinorganic content of spent liquor resulting from such digestion in amanner to produce sulphide and carbonate, recovering the smelt-x edinorganiccompounds in water. earbonat,

ing the smelt solution with carbon dioxide, burning the hydrogensulphide resulting froms'uch carbonation andrecovering the sulphurdioxide thereby produced, acidi-'- 4 fying the carbonated solution withdigester relief gas, recovering and utili'zin the-carbon dioxideliberated in such acidification for the carbonation ofother smeltsolution, treating said carbonated solution with sulphur burner as andthe products ofconlbustion ofsai 'hdrogen sulphide,,'and finallfy addingrelie gas thereto to produce a resh acid cooking liquor having a highfree sg 'content. 33. A, process which comprises digesting rawoellulosie material in a sulphurousaci solution of a soluble alkali oralkaline earth 31. A process which comprises digesting ing the smeltsolution with a strong carbon geste'r relief gas, recovering andutilizing aqueous solution,

. sulphur dioxide,

sulphite, recovering sulphur dioxide from the acid spent liquorresulting from such digestion, concentrating and burning the combustiblecontent and smelting the inorganic content of such spent liquor in amanner to produce sulphide and carbonate,'recovering the smcltedinorganic compounds in water, carbonating the smelt solution, burningthe hydrogen sulphide resultingi'ro'm such carbonation and recoveringthe sulphur dioxide thereby produced, acidifying the carbonated solutionwith digester relief gas, utilizing the carbon dioxide liberated in suchacidification for the carbonationof other smelt solution, and furthertreating said acidified solution with sulphur burner gas, the productsof combustion of the hydrogen sulphide, and the sulphur dioxiderecovered from the acid spent liquor. v

34. A cyclic process which comprises concentrating spent liquorresulting from the digestion of raw cellulosic material in a sulphurousacid solution of a soluble alkali sul-- phite or alkaline earthsulphite, smelting the lnorganic content of such liquor in a reducingatmosphere to produce carbonate and sulcarbon dioxide resulting fromsuch acidification 'in the aforesaid carbonation of. the,

smelted and recovered, sulphide,

35. That process WhlCh comprises smeltingthe mineral content of spentliquor, result-' a ing from the digestion of raw cellulosic material inan alkaline sulphite or alkaline earth'sulphite cooking liquor, toproduce mineral' sulphide and mineral carbonate, re-

covering such sulphide and carbonate in an phide, treating theresultingsolution with sulphur dioxide to produce a sulphite liquor,

recovering carbon dioxide resulting from -such acidification, and usingsuch recovered treating such solution with carbon dioxide to carbonatethe mineral sulno 36. That process which comprises smelt ing the mineralcontent of 5 out liquor, resulting from the digestion o raw cellulosic'.

material in analkaline sulphite or alkaline earth sulphitecooking-liquor, to produce mineral sulphide and mineral carbonate, re-'covering such sulphide and carbonate infan aqueous solution,treating'such solution with carbon dioxide to carbonate the mineralsulphide, treating the resulting solution with sulphur dioxide toproduce a sulphite liquor, recovering hydrogen sulphidejfroi'n suchcarbonation, and burning the same to produce recovering carbon dioxideresulting from such acidification, using such last mentioned sulphurdioxide in the acidi fication of said sulphite liquor.

37. A process for recovering and utilizing the products produced inrecovering the base 1; compound from spent sulphite liquors in forming afresh sulphite cooking liquor,

which comprises treating a carbonate solution with sulphur dioxide toconvert it to a'normal sulphite solution,'recovering the carbon dioxidearising from such treatment and carbonating therewith a sulphite smeltsolution comprising sulphide to a carbonate solution, thereby liberatinghydrogen sulphide, recovering and burning such hydrogen sulphide tosulphur dioxide, and acidifying the normal sulphite solution with therecovered sulphur dioxide.

38. A process which comprises cooking raw cellulosic material in analkaline solution of sodium sulphite; separating the pulp from the spentcooking liquor: smelting the inorganic mineral content and burning thecombustible content of such spent liquor, recovering the inorganicsmelted compounds; and passing the products of combustion from suchsmelting operation in contact with like spent liquor, for the recoveryof the soluble content of such products of combustion.

39. The cyclic process for producing pulp from wood which comprisescooking wood in an acid liquor containing a sulfite of an alkali.separating a residual liquor from the resulting fibrous material, dryingthe residual liquor, carbonizing organic constituents of the liquor.dissolving from the resulting product soluble compounds including alkalicarbonate and alkali sulfide, subiecting the dissolved compoundsto aregulated oxidizing treatment to convert the sulfide into sulfiteunder'conditions to substantially prevent the formation of alkali'thiosulfata'acidifying the resulting sulfite solution. to produce acooking liquor substantially free from thiosulfate, and cooking morewood with said liquor.

40. The cyclic process for producing pulp from wood which comprisescooking wood in a liquor containing a sulfur compound of an alkali.separating the residual liquor from the resulting fibrous material.drying the residual liquor, burning dried carbonaceous constituents ofthe liquor, dissolving from the resultin ash soluble compounds includingalkali sulfide and alkali carbonate, sub

jecting the alkali sulfide to a treatment to remove the sulfide-sulfur,oxidizing it to form sulfur dioxide, and recombining the sulfur dioxideso formed with the alkali compounds, forminga cooking liquor from theresulting sulfite solution, and cooking more wood with said liquor.

41. A process which comprises cooking raw cellulosic material in analkaline solution of sodium sulfite; separating the pulp from the spentcooking liquor; smeltingthe inorganic mineral content and burning thecombustible content of suchtspent liquor in a reducing atmosphere toproduce sodium sulfide; and recovering the inorganic compounds for reusein the cooking of other cellulosic material.

42. A process which comprises cooking raw cellulosic material in analkaline cooking liquor containing sodium sulfite; separating the pulpfrom the spent cooking liquor;

burning the combustible content and smelting the inorganic mineralcontent of such spent liquor in a reducing atmosphere to form sodiumsulfide; recovering the sodium sulfide in water; carbonating the sodiumsulfide of the solution to sodium carbonate; and

acidifying the carbonate solution with sulfur dioxide. v

4;3. A process which comprises cooking raw cellulosic material in analkaline solution of sodium sulfite; separating the pulp from the spentcooking liquor; burning the com bustible content and smelting theinorganic mineral content of such spent liquor in a reducing atmospherein a manner to produce sodium sulfide and sodium carbonate; carbonatingthe sodium sulfide of the smelt solution to sodium carbonate; acidifyingthe whole sodium carbonate solution with sulphur dioxide to convert saidsodium carbonate to sodium sulfite; and recovering and utilizing thecarbon dioxide liberatedin such acidification in the carbonation ofother smelt liquor. r

44. A process which comprises cooking raw cellulosic material in analkaline'solution of sodium sulphite separating the pulp from the spentcooking liquor; burning the combustible content and smelting theinorganic mineral content of such spent liquor in a reducing atmospherein a manner to produce sodium sulphide and sodium carbonate; carbonatingthe smelt solution; and recovering the sulphur to the hydrogen sulphideliberated in such carbonation in the form of a sodium salt.

45. A process which comprises cooking raw cellulosic material in analkaline solution of sodium sulphite; separating the pulp from the spentcooking liquor; burning the combustible content and smeltingtheiinorganio mineral content of such spent liquor in a reducingatmosphere in a manner to produce,

' raw cellulosic material in an alkaline solution of sodium sulphite;separating the pulp from the spent cooking liquor; burning the com- 1smelting the inorganic content of spent liquor resulting from thedigestion of raw cellulosic material in an alkaline solution of sodiumsulphite in a manner to produce sodium sulphide and sodium carbonate;recovering the smelted inorganic compounds in water; carbonating thesmelt solution; recovering the sulphur of the hydrogen sulphideliberated in such carbonation in the form of a sodium salt; acidifyingthe carbonate solution with sulphurous acid; and recoveringand'utilizing the carbon dioxide liberated in such acidification in thecarbonation of other smelt liquor.

48. A process which comprises concentrating and burning the combustiblecontent and smelting the inorganic mineral content of spent liquorresulting from the digestion of raw 'eellulosic material iii an alkalinesolution of sodium sulphite in a manner to produce sodium sulphide andsodium carbonate; recoverlng the smelted inorganic compounds I in water;ca-rbonating the smelt solution; re-

covering the sulphur of the hydrogen sulphide liberated in suchcarbonation in the form of a sodium-sulphur compound; acidifying thecarbonate solution with sulphur.

dioxide; and recovering and utilizing the carbon dioxide liberated insuch acidification in the carbonation of other smelt liquor.

49. A process which comprises concentrating and burning the combustiblecontent and smelting the inorganic mineral content of' spent liquorresulting from the digestion of raw cellulosic material in an alkalinesolution of sodium sulphite in a manner to. produce sodium sulphide andsodium carbonate; recovering the smelted inorganic compounds in water;carbonating the smelt solution with substantially pure carbon dioxideand controlling such carbonation to produce substantially pure hydrogensulphide: recovering and burning such hydrogen sulphide and recoveringthe products of combustion; acidifying the carbonate solution withasulphurous aci solution formed in part from said recovered sulphurdioxide and the products of combustion of sulphur-bearing material;

controlling such acidification to yield a sub;

stantially pure carbon dioxide; and recovering and utilizing such carbondioxide in the carbonation of other smelt liquor.

50. A process which comprises concentrating and burning the combustiblecontent and smeltmgthe inorganic mineral content of teasers spent liquorresulting from the digestion of raw cellulosic material in an alkalinesolution of sodium sulphite in a manner to produce sodium sulphide andsodium carbonate; recovering the smelted inorganiccompounds in water;oarbonating the smelt solution with substantially pure carbon dioxideand controlling such carbonation to produce substantially pure hydrogensulphide; recovering the sulphur of the hydrogen sulphide liberated insuch carbonation in theform of a sodium salt; acidifying the carbonatesolution with sulphurous acid formed from the products of combustion ofsulphur-bearing material; controlling such acidification to produce asubstantially pure carbon dloxide;

and recovering and utilizing such carbon dioxide in the carbonation ofother smelt liquor.

51. A process which comprises concentrating and burning the combustiblecontent and smelting the inorganic content of spent li quor resultingfrom the digestion of raw cellulosic material in an alkaline liquorcontaining sodium sulphite in a manner to produce sodium sulphide andsodium carbonate; recovering the smelted inorganic compounds in water;carbonating the smelt solution with substantially pure carbon dioxide;and controlling such carbonation to produce substantially pure ,hydrogensulphide; recovering such hydrogen sulphide; acidifying the carbonatedsolution with substantially pure sulphur dioxide to convert the sodiumcarbonate to sodium sulphite; controlling such acidification to producea substantially pure carbon dioxide; utilizing such carbon dioxide inthe carbonation of'other smelt solution; treating a sodium compoundemployed for making up losses in the cycle for the production of sodiumsulphide; utilizing the latter in producing a cooking liquor comprisingsodium sul- 'phite and sodium sulphide; and employing such cookingliquor for the digestion of other raw cellulosic material. A.

52. A process which comprises digesting raw cellulosic material in analkaline liquor containing sodium sulphite; concentrating and burningthe combustible content and smelting the inorganic content ofspentliquor resulting from such digesgion in a main ner to producesodium sulphi e and sodium carbonate; recovering the inorganic smeltedcompounds in water; carbonating the smelt solution with carbon dioxideand controlling such carbonation to produce substantially pure hydrogensulphide and to effect a conversion of substantially all the sodiumsulphide to sodium, carbonate; recovering the sulphur of such hydrogensulphide in the formof a sodium salt; acidifying. the sodium carbonate.solution with sulphur dioxide and controlling such acidification toproduce a substantially pure carbon dioxide and a sodium sulphitesolution, and utilizing the carbon dioxide obtained in such'acidification for the carbonation of other smelt solution.

53. A process which comprises digesting raw cellulosic material in analkaline cook ing liquor containing sodium sulphite in solution;separating the pulp from the spent cooking liquor; smelting theinorganicmineral content and burning the combustiblecontent of such spent liquorin a manner to produce sodium sulphide and sodium carbonate; recoveringthe smelted inorganic compounds in Water; carbonating the smelt solutionwith carbon dioxide; acidifying the carbonate solution with sulphurdioxide to produce .a solution of sodium sulphite; recovering thehydrogen sulphide liberated in such treatment in the form of a sodiumsalt; and adding sodium constituents to one of the liquors of the cyclein the form of an alkaline sodium compound for making up losses in thecycle.

54. A process Which comprises cooking raw cellulosic material in analkaline solution of sodium sulphite and sodium sulphide; separating thepulp from the spent cooking liquor; smelting the inorganic mineralcontent and burning the combustible content of such spent liquor in areducing atmosphere to produce sodium sulphide; and recovering theinorganic smelted compounds for reuse in the cooking of other cellulosicmaterial.

55. A process which .comprises cooking j raw cellulosic material in analkaline cooking liquor containing sodium-sulphur compounds; separatingthe pulp from the spent. cooking liquor; burning the combustible contentand smelting-the inorganic mineral 0011- I tent of such spent liquor ina reducing atmosphere to form sodium sulphide; recovering the sodiumsulphide in water; carbonating the sodium sulphide of the solution tosodium carbonate; and acidifying the carbonate solution with sulphurdioxide.

In'testimony whereof we aflix our signatures.

LINN BRADLEY. EDWARD P.- MOKEEFE.

